Search

Phosphorus (P) is a finite resource and its reuse in organic fertilisers made from biowaste and manure should therefore be encouraged. The composition of solid organic fertilisers (SOFs) depends on the type of feedstock and processing conditions, and this may affect P speciation and hence P availability. Phosphorus speciation was assessed in eighteen different SOFs produced from biowaste and digestate. Available P was determined in 10 mM CaCl2 extracts at a fixed pH of 5.5 and at a fixed total P concentration in the suspension. P was dominantly present as inorganic P (&gt, 80% of total P). There was a strong variation in the Fe content of the SOFs and hence in the fraction of P bound to reactive Fe/Al-oxides (PFe). The fraction of total P soluble at pH 5.5 correlated negatively with PFe pointing to fixation of P by metal salts added during processing, or by soil mineral particles in case garden waste was processed. Therefore, the use of iron salts in processing plants should be avoided. In addition, the presence of P in poorly soluble precipitates lowered the fraction of easily available P. Overall, this study shows that Pt alone is not a good indicator for the agronomic efficiency of SOFs due to large differences in P speciation among SOFs.

Phosphorus (P) is an essential plant nutrient. However, our understanding of the complex interactions between soil P availability, environment, management and crop growth is still limited. We used unique historic and recent soil and crop data spanning more than a century combined with a process-based crop model to analyze the impact of P fertilizer omission and P fertilization on the biomass production of five crops. The long-term field experiment at Dikopshof, Germany, was established in 1904 with a 5-year crop rotation of sugar beet, winter wheat, winter rye, clover and oat/potato (potato replaced oat in 1953) on a fertile Luvisol. Averaged over the period from 1906 to 2018, the yield loss due to P omission was low for winter wheat and winter rye (7-8 %). In contrast, yield losses for sugar beet, clover and potato were relatively high (15-24 %). The yield loss from P fertilizer omission in comparison to the reference treatment (rotation mean excluding oat/potato) increased until the middle of the last century from 7% to 18 %, but subsequently decreased to 13 %. Trend and correlation analyses suggest that this decrease was related to an increase in air temperatures in especial during spring and a lower yield loss under P omission. Crop model simulations showed decreasing topsoil organic carbon concentrations after the 1930ies as manure was discontinued in 1942 but also due to increasing air temperatures. The increase in plant-available topsoil P concentrations during the last decades was one of the main factors offsetting yield losses despite P fertilizer omission. Our study suggests that climate change and, in particular, a marked increase in temperature since the middle of the last century most likely influenced soil P dynamics with a significant impact on crop production.

In order to mitigate nutrient pollution in surface runoff more sustainably, the finite capacity for phosphorus (P) sequestration in best management practices (BMP) that rely heavily on sorption processes must be addressed. These BMP include sand filters, bioretention cells, and several types of constructed wetland. This study investigated facilitated microbial reduction of iron-based filtration substrates to promote controlled release of P previously sequestered by the BMP, P harvest for recycling, and rejuvenation of the substrate sorption capacity. Total dissolved P was well correlated with total dissolved iron during the reduction process, indicating that microbial iron reduction was capable of releasing previously sequestered P from substrates. Furthermore, results indicated that a sufficient carbon source was necessary but addition of a microbial culture was not necessary to facilitate iron reduction. While a large percentage of the previously sequestered P was removed, the process was much slower than initial sequestration of P by adsorption, and further research is needed to promote a more rapid release of P in order to optimize the rejuvenation process for field application. NSF 0649079

peer-reviewed Phosphorus (P) loss from soils to water can be a major pressure on freshwater quality and dairy farming, with higher animal stocking rates, may lead to potentially greater nutrient source pressures. In many countries with intensive agriculture, regulation of P management aims to minimise these losses. This study examined the P transfer continuum, from source to impact, in a dairy-dominated, highly stocked, grassland catchment with free-draining soils over three years. The aim was to measure the effects of P source management and regulation on P transfer across the nutrient transfer continuum and subsequent water quality and agro-economic impacts. Reduced P source pressure was indicated by: (a) lower average farm-gate P balances (2.4 kg ha−1 yr−1), higher P use efficiencies (89%) and lower inorganic fertilizer P use (5.2 kg ha−1 yr−1) relative to previous studies; (b) almost no recorded P application during the winter closed period, when applications were prohibited, to avoid incidental transfers; and (c) decreased proportions of soils with excessive P concentrations (32–24%). Concurrently, production and profitability remained comparable with the top 10% of dairy farmers nationally with milk outputs of 14,585 l ha−1, and gross margins of € 3130 ha−1. Whilst there was some indication of a response in P delivery in surface water with declines in quick flow and interflow pathway P concentrations during the winter closed period for P application, delayed baseflows in the wetter third year resulted in elevated P concentrations for long durations and there were no clear trends of improving stream biological quality. This suggests a variable response to policy measures between P source pressure and delivery/impact where the strength of any observable trend is greater closer to the source end of the nutrient transfer continuum and a time lag occurs at the other end. Policy monitoring and assessment efforts will need to be cognisant of this.